Arrangement, method, and current measurement device for measuring a current in a conductor

ABSTRACT

A method, an arrangement, and a current measurement device with which a signal that characterizes a fault current in an electrical conductor having at least three conductor ends can be produced in a particularly simple fashion. In particular, a current measurement device is provided for measuring a current in a conductor. The current measurement device includes at least one measurement value input and at least one measurement value output, and has an arithmetic unit that adds a current measurement value corresponding to the current to a measurement value present at the at least one measurement value input. A resulting summation current measurement value is output at the at least one measurement value output.

FIELD OF THE INVENTION

The present invention relates to an arrangement, method and device formeasuring a current in a conductor.

SUMMARY

An object of the present invention is to provide a method that isparticularly simple to execute for producing a signal that characterizesa fault current in an electrical conductor that has at least threeconductor ends. In this context, a fault current is understood to be acurrent that flows out of the conductor, or that flows into theconductor, at a fault point of the conductor, for example ashort-circuit point, and thus not at one of the conductor ends.

In order to achieve this object, according to the present invention, amethod is provided for producing a fault signal that characterizes afault current of an electrical conductor that has at least threeconductor ends, using current measurement devices that are arranged insuch a way that one of the current measurement devices is attached ateach conductor end of the conductor and the current measurement devicesare connected via data lines. The method the current in the respectiveconductor ends is measured using the current measurement devices, andcurrent measurement values are formed. A measurement value, formed fromthe current measurement values of the other current measurement devicesusing addition that respects the sign, is transmitted to a selectedcurrent measurement device, using the selected current measurementdevice, an overall current value is formed from the current measurementvalues thereof and the measurement value, using addition that respectsthe sign, and the fault signal, is produced using the selected currentmeasurement device if the absolute value of the overall current valueexceeds a predetermined threshold value. The sign-respecting addition ofthe current measurement values can take place in the time domain or inthe frequency domain. If the method according to the present inventionis used in a three-phase alternating current system, the method isexecuted separately for each phase, i.e. for each phase conductor; inthis context, each phase can be switched off individually in the case ofa fault current.

An advantage of the method according to the present invention is that itis very fast, because in the method, the current measurement values ofthe other current measurement devices are first combined, bysign-respecting addition, to form one measurement value, andsubsequently only this measurement value is transmitted to the selectedcurrent measurement device. Since only this single measurement valueneed be transmitted to the selected current measurement device, theoverall quantity of data to be transmitted is very small; this resultsin the particularly high speed of the method according to the presentinvention, since the smaller the amount of data to be transmitted, theless is time required for this. In addition, only a single computationalstep need be executed in the selected current measurement device,consisting in the addition of the transmitted measurement value to themeasured current measurement value of the selected current measurementdevice; the transmission of the previously determined measurement valuetherefore relieves the selected current measurement device of furthercomputational steps, likewise resulting in an increase in speed.

The object is also achieved by a method according to the presentinvention for producing a fault signal that characterizes a faultcurrent of an electrical conductor having at least three conductor ends,using current measurement devices arranged in such a way that one of thecurrent measurement devices is attached to each conductor end of theconductor and the current measurement devices are connected via datalines. In the method the current in the respective conductor ends ismeasured using the current measurement devices, with formation ofcurrent measurement values, and a measurement value, formed from thecurrent measurement values of a first group of the remaining currentmeasurement devices by sign-respecting addition, is transmitted to aselected current measurement device, and an additional measurementvalue, formed from the current measurement values of a second group ofthe remaining current measurement devices by sign-respecting addition,is transmitted to the selected current measurement device. The secondgroup contains all current measurement devices except for the selectedones and the current measurement devices of the first group. Using theselected current measurement device, an overall current value is formedfrom the current measurement values thereof and the two measurementvalues through sign-respecting addition, and the fault signal isproduced using the selected current measurement device if the absolutevalue of the overall current value exceeds a predetermined thresholdvalue. The advantages cited in connection with the first method alsohold for the second method according to the present invention. Aparticular advantage of the second method, is that in this method thecurrent measurement devices can be divided into two groups and aseparate measurement value can be formed for each of the two groups.This can, for example, be advantageous if the two groups of currentmeasurement devices are separated from one another by a large spatialdistance and the formation and transmission of a single measurementvalue to the selected current measurement device would cause aparticularly high expense.

Moreover, an arrangement according to the present invention is providedwith which a fault signal characterizing a fault current in anelectrical conductor having at least three conductor ends can be formedin a particularly simple fashion.

This object is achieved by an arrangement for producing a fault signalthat characterizes a fault current of an electrical conductor having atleast three conductor ends. A current measurement device, attached toeach conductor end of the conductor, measures the current in itsrespective conductor end with formation of a current measurement value.The current measurement devices in the arrangement are connected to oneanother electrically by means of data lines in a chain-type structure insuch a way that each internal current measurement device in the chain isconnected, with a measurement value input, to a measurement value outputof the current measurement device arranged upstream therefrom, and isconnected, with a measurement value output, to a measurement value inputof the current measurement device arranged downstream therefrom. A firstcurrent measurement device of the two current measurement devicesarranged externally in the chain is connected, with its measurementvalue output, to a measurement value input of the internal currentmeasurement device arranged downstream therefrom. The second of the twoexternal current measurement devices is connected, with a measurementvalue input, to the measurement value output of the internal currentmeasurement device arranged upstream therefrom. Each internal currentmeasurement device has an arithmetic unit that adds, in sign-respectingfashion, its current measurement value to a measurement value, presentat its measurement value input, of the respective upstream currentmeasurement device, so as to form a summation current measurement value,and outputs the summation current measurement value as a measurementvalue at its measurement value output. The second external currentmeasurement device has a control unit that outputs the fault signal assoon as an overall current value, formed by sign-respecting additionfrom the measurement value of the upstream internal current measurementdevice and its current measurement value, exceeds a predeterminedthreshold value. An advantage of this arrangement is the particularlyhigh speed with which the fault signal is produced, since not all thecurrent measurement values of the other current measurement devices aretransmitted individually to the second external current measurementdevice. Instead, only a single measurement value is transmitted thatcontains the current sums of the remaining current measurement devices.This results in a particularly rapid production of the fault signal,because the overall quantity of data to be transmitted to the secondexternal current measurement device is relatively small, since only asingle measurement value is to be transmitted. An additional advantageof the arrangement according to the present invention is that onlyrelatively few data lines are necessary for connecting the currentmeasurement devices; given a line having N conductor ends, in thechain-type arrangement of the current measurement devices only (N−1)data lines are required, whereas, in contrast, given an arrangement inwhich all current measurement devices are connected to one anotherN*(N−1) data lines are required.

In order that, in addition to the second external current measurementdevice, at least one internal current measurement device can alsoproduce the fault signal, within the scope of a development of thearrangement, the internal current measurement devices may be connectedto one another in such a way that an additional measurement value inputof an internal current measurement device is connected to an additionalmeasurement value output of the internal current measurement devicearranged downstream therefrom, and an additional measurement valueoutput of an internal current measurement device is connected to anadditional measurement value input of the internal current measurementdevice arranged upstream therefrom. The first external currentmeasurement device is connected, with a measurement value input, to anadditional measurement value output of the internal current measurementdevice arranged downstream therefrom. The second external currentmeasurement device is connected, with a measurement value output, to anadditional measurement value input of the internal current measurementdevice arranged upstream therefrom. Each internal current measurementdevice has an additional arithmetic unit that adds, in sign-respectingfashion, the current measurement value of its own current measurementdevice to an additional measurement value, present at its additionalmeasurement value input, of the downstream current measurement device,so as to form an additional summation current measurement value, andoutputs the resulting additional summation current measurement value atits additional measurement value output as an additional measurementvalue. At least one of the internal current measurement devices has acontrol unit that produces the fault signal as soon as the overallcurrent value, formed by sign-respecting addition from the measurementvalues present at its two measurement value inputs and its measuredcurrent measurement value, exceeds the predetermined threshold value.The advantage of this arrangement is that a plurality of currentmeasurement devices of the arrangement are able to produce the faultsignal, since all the current measurement devices are provided with therequired items of current information; in such an arrangement, 2*(N−1)data lines are then required.

In order that the fault signal can also be produced using the firstexternal current measurement device, the first external currentmeasurement device may have a control unit that produces the faultsignal as soon as the overall current value—formed by sign-respectingaddition from the measurement value present at its measurement valueinput and its measured current measurement value—exceeds thepredetermined threshold value.

A particularly high degree of reliability can be achieved in thearrangement according to the present invention if the two externalcurrent measurement devices are connected with one another by at leastone additional data line via which the overall current value istransmitted. This is because in such an arrangement the respectivelydetermined overall current value can be transmitted between the twoexternal current measurement devices for monitoring purposes; forexample, the two external current measurement devices can check thereadiness for operation of the overall arrangement by comparing theirrespective overall current values. An additional advantage of theadditional data line is that the arrangement according to the presentinvention can continue to be operated even if one of the data lines isinterrupted by a disturbance.

Within the scope of the present invention, a current measurement deviceis also proposed that can be used in the method or in the arrangementaccording to the present invention. This is a current measurement devicefor measuring a current in a conductor having at least one measurementvalue input and at least one measurement value output, as well as anarithmetic unit that adds a current measurement value corresponding tothe current to a current measurement value present at the at least onemeasurement value input, and outputs the resulting summation currentmeasurement value at the at least one measurement value output. Theadvantage of the current measurement device according to the presentinvention is that it has an arithmetic unit with which, for example,summation current measurement values can be formed, as was explainedabove in connection with the method or the arrangement according to thepresent invention. The advantages described above in connection with themethod and with the arrangement thus hold in corresponding fashion forthe current measurement device according to the present invention.

In order to facilitate the installation of the current measurementdevice according to the present invention, it is proposed, within thescope of a development of the current measurement device, that thearithmetic unit have a device with which the sign of the currentmeasurement value can be changed. Such a current measurement device hasthe advantage that when connecting the current measurement device to aconductor or to a conductor end no attention need be paid to thedirection of the current in the conductor or conductor end, because thesign of the current measurement value determined by the currentmeasurement device can be changed if necessary, so to speakretroactively. This may be for example, important with respect to thesign-respecting addition of the current measurement values in theinventive method for producing a fault signal, since in the formation ofa summation current measurement value the signs are of course to betaken into account.

If in addition a fault signal is also to be formed using the inventivecurrent measurement device, may be as advantageous if the currentmeasurement device has a control unit that outputs a signal for a faultcurrent as soon as the summation current measurement value exceeds apredetermined threshold value.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an exemplary embodiment for an arrangement for theexecution of the method according to the present invention.

FIG. 2 shows an exemplary embodiment for an arrangement according to thepresent invention.

FIG. 3 shows an exemplary embodiment for a current measurement deviceaccording to the present invention having an arithmetic unit and acontrol unit.

DETAILED DESCRIPTION

FIG. 1 shows an arrangement 3 for monitoring an electrical conductor 6for a fault current. Electrical conductor 6 has a total of fiveconductor ends, including a first conductor end 9, a second conductorend 12, a third conductor end 15, a fourth conductor end 18, and a fifthconductor end 21. A current measurement device is attached to each ofconductor ends 9, 12, 15, 18, and 21, the current measurement devicesbeing connected with one another via data lines, for example opticalglass fibers. In this context, a selected first current measurementdevice 30 is connected to first conductor end 9 and additional currentmeasurement devices 33, 36, 39, and 42 are connected respectively to theremaining conductor ends 12, 15, 18, and 21.

Specifically, first current measurement device 30 is connected with itsmeasurement value input E30 a to a measurement value output A33 a offirst additional current measurement device 33 (referred to in thefollowing as second current measurement device 33 for short). Upstreamfrom this current measurement device, the second of the additionalcurrent measurement devices 36 (referred to in the following as thirdcurrent measurement device 36 for short) is connected, with itsmeasurement value output A36 a, at a measurement value input E33 a.

Moreover, first current measurement device 30 is connected, with anadditional measurement value input E30 b, to a measurement value outputA39 a of the third of the additional current measurement devices 39(referred to below as fourth current measurement device 39 for short).Upstream from this current measurement device, the fourth of theadditional current measurement devices 42 (referred to in the followingas fifth current measurement device 42 for short) is connected, with itsmeasurement value output A42 a, at a measurement value input E39 a.

Five current measurement devices 30, 33, 36, 39, and 42 are thusconnected to one another in a chain-type structure, third currentmeasurement device 26 and fifth current measurement device 42 formingexternal current measurement devices in the chain, and first currentmeasurement device 30, second current measurement device 33, and fourthcurrent measurement device 39 forming internal current measurementdevices in the chain.

Arrangement 3 is used to monitor electrical conductor 6 for a faultcurrent in the manner described below.

Using a clock (pulse) generator (not shown), a clock signal istransmitted to all current measurement devices. This clock signalensures that all current measurement devices determine the respectivecurrent in their conductor end at respectively identical points in time.

After all the current measurement devices have measured, at one point intime, currents IA′, . . . , IE′ in respective conductor ends 9, 12, 15,18, 21, the following is carried out:

Current measurement value IC of third current measurement device 36,corresponding to current IC′ in conductor end 15, is outputted atmeasurement value output A36 a of third current measurement device 36,and is transmitted to measurement value input E33 a of second currentmeasurement device 33. Using an arithmetic unit (not shown in FIG. 1),this second current measurement device 33 adds current measurement valueIC, transmitted from third current measurement device 36, to currentmeasurement value IB, which corresponds to current IB′ flowing throughconductor end 12 of second current measurement device 33, forming asummation current measurement value IC+IB. This summation currentmeasurement value IC+IB is transmitted to first current measurementdevice 30 from second current measurement device 33.

Fifth current measurement device 42 at fifth conductor end 21, as wellas fourth current measurement device 39 at fourth conductor end 18,operate in exactly the same manner as the second and the third currentmeasurement device, i.e., each adds, in sign-respecting fashion, thecurrent measurement value of its own respective current measurementdevice to a current measurement value—present at its measurement valueinput—of the current measurement device that may respectively bearranged upstream, taking into account the respective direction ofcurrent, and outputs the resulting summation current measurement valueat its measurement value output as a measurement value.

A measurement value composed of current measurement values IB and ICthus arrives at the one measurement value input E30 a of first currentmeasurement device 30, and an additional measurement value, composed ofcurrent measurement values IE and ID, arrives at additional measurementvalue input E30 b of first current measurement device 30.

An overall current value is thereupon formed in first currentmeasurement device 30 by addition of the one measurement value and theadditional measurement value, as well as the current measurement valueIA that indicates the current IA′ in conductor end 9; this overallcurrent value is equal to IA+IB+IC+ID+IE.

In accordance with the Kirchhoff laws, overall current value IA+IB+. . .+IE must be equal to 0 if no fault current has occurred; if the overallcurrent value is not equal to 0, or if it exceeds a predeterminedthreshold value, a fault current has occurred. Here a fault current isunderstood to be a current flowing from conductor 6, or into conductor6, at a fault point, for example a short-circuit point, and thus not atone of conductor ends 9, 12, 15, 18, or 21. Both types of fault currentare reflected in the overall current value of current measurement device30, which can be determined by comparison of the overall current valuewith the threshold value, which is approximately equal to 0.

To sum up, on the basis of the overall current value in selected firstcurrent measurement device 30 it is determined, by comparison with thethreshold value, whether a fault current has occurred. In this context,for example in a direct-current system, it is possible not only todetermine whether a fault has occurred at all, but in addition it is ofcourse also possible to determine the type of the fault, if after thecomparison of the overall current value with the predetermined thresholdvalue with respect to absolute value the sign of the overall currentvalue is also evaluated. This is because, according to its allocation toa direction of current, the sign indicates whether the fault currentflowed into conductor 6 or out of conductor 6.

FIG. 2 shows an exemplary embodiment of an example arrangement accordingto the present invention. Current measurement devices 100, 103, 106, and109 are connected to one another electrically by means of data lines 112to form a chain-type structure. Here two current measurement devices—100and 109—are located at the outer end of the chain, and two currentmeasurement devices—103 and 106—are located in the interior of thechain.

First internal current measurement device 103 is connected, with itsmeasurement value input E103 a, to a measurement value output A100 a ofcurrent measurement device 100, which is arranged upstream from device103. A measurement value input E106 a of second internal currentmeasurement device 106 is arranged downstream from first internalcurrent measurement device 103, at its measurement value output A103 a,and a measurement value input E109 a of second external currentmeasurement device 109 is in turn connected downstream from secondcurrent measurement device 106, at its measurement value output A106 a.Moreover, second external current measurement device 109 has ameasurement value output A109 b that is connected with an additionalmeasurement value input E106 b of second internal current measurementdevice 106; this second internal current measurement device 106 ismoreover connected, with an additional measurement value output A106 b,to an additional measurement value input E103 b of first internalcurrent measurement device 103. With an additional measurement valueoutput A103 b, this first internal current measurement device 103 isalso connected with a measurement value input E100 b of first externalcurrent measurement device 100.

Moreover, there is another data line 115—a duplex line between—firstexternal current measurement device 100 and second external currentmeasurement device 109.

In addition, each of current measurement devices 100, 103, 106, and 109is respectively connected to a conductor end of electrical conductor 130(shown only schematically in FIG. 2), which has four conductor ends 120,123, 126, and 129, and measures current IA′, IB′, IC′, or ID′ flowing atits conductor end, with formation of current measurement values IA, IB,IC, or ID. In this context, first external current measurement device100 measures current measurement value or values IA at first conductorend 120, first internal current measurement device 103 measures currentmeasurement value or values IB at second conductor end 123, secondinternal current measurement device 106 measures current measurementvalue or values IC at third conductor end 126, and second externalcurrent measurement device 109 measures current measurement value orvalues ID at fourth conductor end 129.

The arrangement according to FIG. 2 is operated as follows: currentmeasurement value IA, measured using first external current measurementdevice 100, is transmitted to the one measurement value input E103 a offirst internal current measurement device 103 via data line 112. In thisdata line, from its own current measurement value IB and frommeasurement value IA of first external current measurement device 100, asummation current measurement value IA+IB is formed that is transmitted,as measurement value IA+IB, to the one measurement value input E106 a ofsecond internal current measurement device 106. In second internalcurrent measurement device 106, from measurement value IA+IB and its owncurrent measurement value IC, a new summation current measurement valueIA+IB+IC is formed that is transmitted as a measurement value to the onemeasurement value input E109 a of second external current measurementdevice 109. In this current measurement device 109, from measurementvalue IA+IB+IC and from its own current measurement value ID, an overallcurrent value IA+IB+IC+ID is formed; current measurement device 109produces, at a control output that is not depicted, a fault signal S fora fault current if overall current value IA+IB+IC+ID is not equal to 0,or if it exceeds a predetermined threshold value.

Simultaneously, current measurement value ID of second external currentmeasurement device 109 is transmitted, as an additional measurementvalue, to additional measurement value input E106 b of second internalcurrent measurement device 106. In second internal current measurement106, the one measurement value IA+IB of first internal currentmeasurement device 103 is now present at the one measurement value inputE106 a, and additional measurement value ID is now present at additionalmeasurement value input E106 b. From the two measurement values and fromits own measured current measurement value IC, overall current valueIA+IB+IC+ID is formed in current measurement device 106, and the faultsignal is formed as soon as overall current value IA+IB+IC+ID is notequal to 0 or exceeds the predetermined threshold value; fault signal Sis then outputted at a control output (not shown). Moreover, in currentmeasurement device 106, an additional summation current measurementvalue IC+ID is formed from additional measurement value ID—present atadditional measurement value input E106 b—and its own currentmeasurement value IC; the additional summation current measurement valueIC+ID is outputted at additional measurement value output A106 b and istransmitted to first internal current measurement device 103.

In first internal current measurement device 103, the one measurementvalue IA of first external current measurement device 100 is now presentat the one measurement value input E103 a, and additional measurementvalue IC+ID is now present at additional measurement value input E103 b.From the two measurement values IA and IC+ID, and from its own measuredcurrent measurement value IB, overall current value IA+IB+IC+ID isformed in current measurement device 103, and the fault signal is formedas soon as overall current value IA+IB+IC+ID is not equal to 0 orexceeds the predetermined threshold value. Fault signal S is thenoutputted at a control output (not shown). Moreover, in currentmeasurement device 103 an additional summation current measurement valueIB+IC+ID is formed from additional measurement value IC+ID—present atadditional measurement value input E103 b—and its own currentmeasurement value IB, and this additional summation current measurementvalue IB+IC+ID is outputted, at additional measurement value output A103b, to first external current measurement device 100.

In first external current measurement device 100, measurement valueIB+IC+ID of first internal current measurement device 103 is now presentat measurement value input E100 b. In first external current measurementdevice 100, overall current value IA+IB+IC+ID is formed from measurementvalue IB+IC+ID and from its own measured current measurement value IA,and the fault signal is formed as soon as overall current valueIA+IB+IC+ID is not equal to 0 or exceeds the predetermined thresholdvalue; fault signal S is then outputted at a control output (not shown).

To sum up, one measurement value or two measurement values are thustransmitted to each of the current measurement devices, and with thesevalues each of the current measurement devices is able, using its owncurrent measurement value, to determine the overall current value and toproduce the fault signal.

Via additional data line 115, the overall current value is transmittedbetween the two external current measurement devices 100 to and 109 formonitoring purposes; for this purpose, in the two current measurementdevices it is checked whether the overall current value transmitted bythe respective other external current measurement device corresponds toits own overall current value. If this is not the case, an alarm signalis produced indicating a fault in the measurement arrangement. A furtheradvantage of additional data line 115 is that the arrangement accordingto FIG. 2 can also continue to be operated when data line 112 betweentwo adjacent current measurement devices has been interrupted, since insuch a case additional data line 115 can be used as a replacement forinterrupted data line 112.

The one arithmetic unit and the additional arithmetic unit can forexample be formed by a data processing installation or by amicroprocessor arrangement.

FIG. 3 shows an exemplary embodiment of a current measurement devicethat can be used in the arrangements according to FIGS. 1 and 2. Here,for purposes of explanation the current measurement device 103 accordingto FIG. 2 is used as a basis, and, in order to facilitate understandingof FIG. 3, reference characters identical to those used in FIG. 2 areused for components in FIG. 3 that have already been explained inconnection with FIG. 2.

Current measurement device 103 has a current input I103 a and anadditional current input I103 b, with which current measurement device103 is connected to conductor end 123 of conductor 130 according to FIG.2. A measurement unit 73 is connected with the two current inputs I103 aand I103 b, and downstream from this measurement unit 73 there arearranged a summation element 76 as an arithmetic unit with an input E76a, an additional summation element 77 as an additional arithmetic unitwith an input E77 a, and a control unit 78 with an input E78 a.Summation element 76 is connected, with an additional input E76 b, withthe one measurement value input E103 a of current measurement device103, and is connected, with an output A76, with the one measurementvalue output A103 a of current measurement device 103. Additionalsummation element 77 is connected, with an additional input E77 b, toadditional measurement value input E103 b of current measurement device103, and is connected, with an output A77, to additional measurementvalue output A103 b of current measurement device 103.

An additional input E78 b of control unit 78 is connected to the onemeasurement value input E103 a of current measurement device 103; anadditional measurement value input E78 c of control unit 78 is connectedwith additional measurement value input E103 b of current measurementdevice 103.

Using measurement unit 73, current IB′ in conductor end 123 is measured,and a current measurement value IB corresponding to current IB′ isformed. This value arrives at arithmetic unit 76, in which a summationcurrent measurement value IA+IB is formed from this value and from theone measurement value IA at the one measurement value input E103 a, andthis summation current measurement value is transmitted as a measurementvalue to the one measurement value output A103 a of current measurementdevice 103.

Current measurement value IB also arrives at additional summationelement 77, in which an additional summation current measurement valueIB+IC+ID is formed from additional measurement value IC+ID at additionalmeasurement value input E103 b of current measurement device 103 andfrom current measurement value IB, and this additional summation currentmeasurement value IB+IC+ID is outputted as a measurement value at theadditional measurement value output A103 b of current measurement device103.

Moreover, current measurement value IB is transmitted to control unit78, in which an overall current value IA+IB+IC+ID is formed from its owncurrent measurement value IB, the one measurement value IA, andadditional measurement value IC+ID.

In control unit 78, this overall current value IA+. . . +ID is comparedwith a predetermined threshold value that is approximately equal to 0.If the overall current value exceeds the predetermined threshold value,a signal S is outputted at a control signal output S103 of currentmeasurement device 103, indicating a fault current in conductor 130.

Moreover, current measurement device 103 has a terminal Q1 that isconnected with control unit 78. If current measurement device 103 is tobe operated as an external current measurement device 100 or 109according to FIG. 2, the current measurement device can be connected viathis terminal Q1 with the respective other external current measurementdevice via additional data line 115, for the transmission of overallcurrent value IA+. . . +ID. In control unit 78, it is then comparedwhether its own overall current value is equal to the transmittedoverall current value of the other external current measurement device.If this is not the case, an alarm signal A is outputted at an additionalterminal Q2, indicating that a fault has occurred in the measurementarrangement.

The one and the other arithmetic unit 76 and 77, as well as control unit78, can be formed by a data processing installation, for example amicroprocessor arrangement.

What is claimed is:
 1. A method for producing a fault signal thatcharacterizes a fault current of an electrical conductor, the electricalconductor having at least three conductor ends, comprising: providingcurrent measurement devices so that a different one of the currentmeasurement devices is coupled to a respective one of the conductorends, the current measurement devices being connected together via datalines; using the current measurement devices, measuring a current ineach respective one of the conductor ends and forming currentmeasurement values; transmitting a measurement value to a selected oneof the current measurement devices, the measurement value being formedfrom the current measurement values of other ones of the currentmeasurement devices using sign-respecting addition; using the selectedone of the current measurement devices, forming an overall current valuefrom the current measurement values of the selected one of the currentmeasurement devices and the measurement value using sign-respectingaddition; and producing the fault signal using the selected one of thecurrent measurement devices if an absolute value of the overall currentvalue exceeds a predetermined threshold value.
 2. A method for producinga fault signal that characterizes a fault current of an electricalconductor, the electrical conductor having at least three conductorends, comprising: providing current measurement devices so that adifferent one of the current measurement devices is coupled to arespective one of the conductor ends, the current measurement devicesbeing connected together via data lines; using the current measurementdevices, measuring a current in each respective one of the conductorends and forming current measurement values; transmitting a measurementvalue to a selected one of the current measurement devices, themeasurement value being formed from the current measurement values of afirst group of the others of the current measurement devices usingsign-respecting addition; transmitting an additional measurement valueto the selected one of the current measurement devices, the additionalmeasurement value being formed from the current measurement values of asecond group of remaining ones of the current measurement devices bysign-respecting addition, the second group containing all currentmeasurement devices except for the selected one of the currentmeasurement devices and the current measurement devices of the firstgroup; using the selected one of the current measurement devices,forming an overall current value from the current measurement value ofthe selected current measurement device, the measurement value and theadditional measurement value; and producing a fault signal using theselected one of the current measurement devices if an absolute value ofthe overall current value exceeds a predetermined threshold value.
 3. Anarrangement for producing a fault signal that characterizes a faultcurrent of an electrical conductor having at least three conductor ends,comprising: current measurement devices, a different one of the currentmeasurement devices being coupled to a respective one of the conductorends and measuring current in the respective one of the conductor endsto form a respective current measurement value, the current measurementdevices being electrically connected to one another using data lines ina chain structure, the current measurement devices including internalcurrent measurement devices and external current measurement devices,each of the internal current measurement devices has a respectivemeasurement value input connected to a measurement value output of arespective upstream one of the current measurement devices, and has arespective measurement value output coupled to a measurement value inputof a downstream one of the current measurement devices, a first one ofthe external current measurement devices has a measurement value outputconnected to a measurement value input of a downstream one of theinternal current measurement devices, a second one of the externalcurrent measurement devices has a measurement value input connected to ameasurement value output of an upstream one of the internal currentmeasurement devices, each of the internal measurement devices includesan arithmetic unit that adds, in a sign-respecting fashion, a respectivecurrent measurement value to a measurement value, present at therespective measurement value input, of the respective upstream currentmeasurement device, to form a summation current measurement value, andoutputs the summation current measurement value as a measurement valueat the respective measurement value output, and the second one of theexternal current measurement devices has a control unit that outputs thefault signal as soon as an overall current value, formed bysign-respecting addition of the respective measurement value of theupstream one of the internal current measurement devices and arespective current measurement value of the second one of the externalcurrent measurement devices, exceeds a predetermined threshold value. 4.The arrangement according to claim 3, wherein: the internal currentmeasurement devices are connected to one another so that an additionalmeasurement value input of a first one of the internal currentmeasurement devices is connected to an additional measurement valueoutput of a downstream one of the internal current measurement devices,and an additional measurement value output of an additional measurementvalue output of a second one of the internal current measurement devicesis connected to an additional measurement value input of an upstream oneof the internal current measurement devices, the first one of theexternal current measurement devices is connected, via a measurementvalue input, to the additional measurement value output of a downstreamone of the internal current measurement devices, the second one of theexternal current measurement devices is connected, via a measurementvalue output, to the additional measurement value input of an upstreamone of the internal current measurement devices, each one of theinternal measurement devices includes an arithmetic unit that adds, in asign-respecting fashion, a respective current measurement value to anadditional measurement value, present at the additional measurementvalue input of the one of the internal measurement devices of adownstream one of the current measurement devices to form an additionalsummation current measurement value, and outputs the additionalsummation current measurement value at an additional measurement valueoutput of the one of the internal measurement devices as an additionalmeasurement value, and at least one of the internal current measurementdevices includes a control unit that produces the fault signal soon asan overall current value, formed by sign-respecting addition ofmeasurement values present at the measurement value input and theadditional measurement value input of the at least one of the internalcurrent measurement devices and the measured current value of the atleast one of the internal current measurement devices, exceeds thepredetermined threshold value.
 5. The arrangement according to claim 4,wherein: the first external current measurement device includes acontrol unit that produces the fault signal as soon as an overallcurrent value, formed by sign-respecting addition of measurement valuespresent at the measurement value input of the first external currentmeasurement device and the current measurement value of the firstexternal current measurement device, exceeds the predetermined thresholdvalue.
 6. The arrangement according to claim 3, wherein the externalcurrent measurement devices are connected to one another via at leastone additional data line via which the overall current value istransmitted.
 7. A current measurement device for measuring a current ina conductor, comprising: at least one measurement value input; at leastone measurement value output; and an arithmetic unit connected to the atleast one measurement value input and the at least one measurement valueoutput, the arithmetic unit adding a current measurement valuecorresponding to the current to a measurement value present at the atleast one measurement value input to form a summation currentmeasurement value, the arithmetic unit outputting the summation currentmeasurement value at the at least one measurement value output.
 8. Thecurrent measurement device according to claim 7, wherein the arithmeticunit includes a device with which a sign of the current measurementvalue can be changed.
 9. The current measurement device according toclaim 7, further comprising: a control unit connected to the arithmeticunit, the control unit outputting a signal for a fault current as soonas an overall current value, formed with the current measurement valueand the measurement value exceeds a predetermined minimum.